Compressor capacity modulation

ABSTRACT

A pulsed modulated capacity modulation system for refrigeration, air conditioning or other types of compressors is disclosed in which suitable valving is provided which operates to cyclically block flow of suction gas to a compressor. A control system is provided which is adapted to control both the frequency of cycling as well as the relative duration of the on and off time periods of each cycle in accordance with sensed system operating conditions so as to maximize the efficiency of the system. Preferably the cycle time will be substantially less than the time constant of the load and will enable substantially continuously variable capacity modulation from substantially zero capacity to the full capacity of the compressor. Additional controls may be incorporated to modify one or more of the motor operating parameters to improve the efficiency of the motor during periods of reduced load.

More than one reissue application has been filed for the reissue of U.S.Pat. No. 6,206,652. The reissue applications are application Ser. No.11/152,834 (now U.S. Pat. No. RE40,830) and Ser. No. 11/152,836 (thepresent application), all of which are reissue applications of U.S. Pat.No. 6,206,652.

The present application is a continuation-in-part of U.S. applicationSer. No. 08/939,779 filed Sep. 29, 1997, which is now U.S. Pat. No.6,047,557 issued Apr. 11, 2000.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention is directed to a system for modulating thecapacity of a positive displacement compressor such as a refrigerationand/or air conditioning compressor and more specifically to a systemincorporating a valving arrangement for cyclically blocking suction gasflow to the compressor while the compressor is continuously driven.

Capacity modulation is often a desirable feature to incorporate inrefrigeration and air conditioning compressors as well as compressorsfor other applications in order to enable them to better accommodate thewide range of loading to which systems incorporating these compressorsmay be subjected. Many different approaches have been utilized forproviding this capacity modulation feature ranging from controlling ofthe suction inlet flow such as by throttling to bypassing discharge gasback to the suction inlet and also through various types of cylinder orcompression volume porting arrangements.

In multicylinder reciprocating piston type compressors utilizing suctiongas control to achieve capacity modulation, it is common to block theflow to one or more but not all of the cylinders. When activated, thecapacity of the compressor will be reduced by a percentage nominallyequal to the number of cylinders to which suction gas flow has beenblocked divided by the total number of cylinders. While sucharrangements do provide varying degrees of capacity modulation, thedegree of modulation that can be achieved is available only inrelatively large discrete steps. For example, in a six cylindercompressor, blocking suction to two cylinders reduces the capacity by ⅓or 33.3% whereas blocking suction gas flow to four cylinders reducescapacity by ⅔ or 66.6%. This discrete step form of modulation does notallow the system capacity to be matched to the load requirementconditions at all but rather only to very roughly approach the desiredcapacity resulting in either an excess capacity or deficient capacity.As system conditions will rarely if ever match these gross steps ofmodulation, the overall operating system efficiency will not be able tobe maximized.

Compressors in which discharge gas is recirculated back to suction offerquasi-infinite step modulation of the capacity depending upon thevariation and complexity of the bypassing means. However, when dischargegas is recirculated back to suction, the work of compression is lost forthat fraction of the gas recirculated thus resulting in reduced systemefficiency. Combinations of the aforementioned methods enablessubstantially quasi-infinite capacity modulation at slightly betterefficiency but still fails to provide the ability to closely match thecompressor capacity to the load being served.

Other approaches, which can result in selectively disabling thecompression process of one or more of the cylinders of a multi-cylindercompressor, such as cylinder porting, stroke altering or clearancevolume varying methods result in similar step modulation with aresulting mismatch between load and capacity and additionally sufferfrom dynamic load unbalance and hence vibration.

The present invention, however, provides a capacity control arrangementwhich utilizes a pulse width modulation of suction gas flow to thecompressor which enables substantially continuous modulation of thecapacity from 0% up to 100% or full capacity. Thus the capacity outputof the compressor can be exactly matched to system loading at any pointin time. Further, in reciprocating piston type compressors, the suctiongas flow to each of the cylinders may be controlled simultaneously bythis pulse width modulation system so as to eliminate unbalancedoperation of the compressor.

The pulse width modulated compressor is driven by a control system thatsupplies a variable duty cycle control signal based on measured systemload. The controller may also regulate the frequency (or cycle time) ofthe control signal to minimize pressure fluctuations in the refrigerantsystem. The on time is thus equal to the duty cycle multiplied by thecycle time, where the cycle time is the inverse of the frequency.

The pulse width modulated compressor of the present invention has anumber of advantages. Because the instantaneous capacity of the systemis easily regulated by variable duty cycle control, an oversizedcompressor can be used to achieve faster temperature pull down atstartup and after defrost without causing short cycling as conventionalcompressor systems would. Another benefit of the present invention isthat the system can respond quickly to sudden changes in condensertemperature or case temperature set points. The controller adjustscapacity in response to disturbances without producing unstableoscillations and without significant overshoot. This capability is ofparticular advantage in applications involving cooling of display casesin that it allows a much tighter control of temperature within the casethereby enabling the temperature setting to be placed at a higher levelwithout concern that cyclical temperature swings will exceed thetemperatures which are considered safe for the particular goodscontained therein.

Operating at higher evaporator temperatures reduces the defrost energyrequired because the system develops frost more slowly at highertemperatures. This also enables the time between defrost cycles to belengthened.

The pulse width modulated compressor also yields improved oil return.The volume of oil returned to the compressor from the system isdependent in part on the velocity of gas flow to the compressor. In manycapacity modulation systems, the return gas flow to the compressor ismaintained at a relatively low level thus reducing the return oil flow.However, in the present invention the refrigerant flow pulsates betweenhigh capacity and low capacity (e.g. 100% and 0%), thus facilitatingincreased oil return due to the periods of high velocity gas flow.

Additionally, the pulse width modulated blocked suction system of thepresent invention is relatively inexpensive to incorporate into acompressor in that only a single valve assembly is required. Further,because of the system's simplicity, it can be easily added to a widevariety of compressor designs including both rotary and scroll as wellas reciprocating piston type compressors. Also, because the presentinvention keeps the driving motor operating while the suction gas flowis modulated, the stress and strain on the motor resulting from periodicstart-ups is minimized. Additional improvements in efficiency can beachieved by incorporating a motor control module which may operate tocontrol various operating parameters thereof to enhance its operatingefficiency during periods when the motor load is reduced due tounloading of the compressor.

Additional features and benefits of the present invention will becomeapparent to one skilled in the art from the following detaileddescription taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a reciprocating piston type compressorincorporating apparatus by which the suction gas flow to the compressormay be blocked in a pulse width modulated manner in accordance with thepresent invention;

FIG. 2 is a waveform diagram illustrating the variable duty cycle signalproduced by the controller and illustrating the operation at a constantfrequency;

FIG. 3 is a waveform diagram of the variable duty cycle signal,illustrating variable frequency operation;

FIG. 4 is a graph comparing anticipated temperature dynamics of a systememploying the invention with a system of conventional design;

FIG. 5 is a view similar to that of FIG. 1 but showing a rotary typecompressor incorporating the pulse width modulation system of thepresent invention;

FIG. 6 is a section view of the compressor of FIG. 5, the section beingtaken along line 6-6 thereof;

FIG. 7 is a view similar to that of FIGS. 1 and 5 but showing a scrolltype compressor incorporating the pulse width modulation system of thepresent invention;

FIG. 8 is a schematic diagram illustrating the inclusion of a motorcontrol module to modify one or more of the compressor motor operatingparameters during periods of reduced load; and

FIG. 9 is a section view generally illustrating a preferred valvingarrangement for use in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and more specifically to FIG. 1 there isshown a reciprocating piston type refrigeration compressor 10 comprisingan outer shell 12 within which is disposed reciprocating compressorhousing 14 on which is mounted an associated driving motor includingstator 16 having a bore 18 provided therein. A rotor 20 is disposedwithin bore 18 being secured to crankshaft 22 which is rotatablysupported within housing 14 by upper and lower bearings 24 and 26respectively. A pair of pistons 28 and 30 are connected to crankshaft 22and reciprocably disposed in cylinders 32 and 34 respectively. A motorcover 36 is secured in overlying relationship to the upper end of stator16 and includes an inlet opening 38 aligned with a suction inlet fitting40 provided through shell 12. A suction muffler 44 is provided on theopposite side of motor cover 36 and serves to direct suction gas fromthe interior of motor cover 36 to respective cylinders 32, 34 viasuction pipe 42 and head assembly 46.

As thus far described, compressor 10 is a typical hermetic reciprocatingpiston type motor compressor and is described in greater detail in U.S.Pat. No. 5,015,155 assigned to the assignee of the present application,the disclosure of which is hereby incorporated by reference.

A bidirectional solenoid valve assembly 48 is provided in suction pipe42 between suction muffler 44 and head assembly 46. Solenoid valveassembly operates to control suction gas flow through pipe 42 to therebymodulate the capacity of motor compressor 10. An exemplary valveassembly suitable for this application is described in greater detailbelow.

In order to control solenoid valve assembly 48, a control module 50 isprovided to which one or more suitable sensors 52 are connected. Sensors52 operate to sense operating system conditions necessary to determinesystem loading. Based upon signals received from sensors 52 and assumingsystem conditions indicate a less than full capacity is required,control module 50 will operate to pulse solenoid valve assembly 48 so asto alternately allow and prevent the flow of suction gas through conduit42 to compression cylinders 32 and 34 while the motor continues to drivepistons 28 and 30. The variable duty cycle control signal generated bythe control module 50 can take several forms. FIGS. 2 and 3 give twoexamples. FIG. 2 shows the variable duty cycle signal in which the dutycycle varies, but the frequency remains constant. In FIG. 2, note thatthe cycle time, indicated by hash marks 53, are equally spaced. Bycomparison, FIG. 3 illustrates the variable duty cycle signal whereinthe frequency is also varied. In FIG. 3, note that the hash marks 53 arenot equally spaced. Rather, the waveform exhibits regions of constantfrequency, regions of increasing frequency and regions of decreasingfrequency. The variable frequency illustrated in FIG. 3 is the result ofthe adaptive modulation of the cycle time to further optimize systemoperation. An adaptive modulation control system is described in greaterdetail in assignee's copending application Ser. No. 08/939,779 thedisclosure of which is hereby incorporated by reference.

Given the speed of rotation of the compressor there would be asubstantial number of compression cycles during which no suction gaswould be supplied to the compression chambers. However thereafter therewould be another number of compression cycles during which full suctiongas flow would be supplied to the cylinders. Thus on average, the massflow would be reduced to a desired percentage of full load capacity.Because the mass flow to each cylinder is reduced at the same time, theoperating balance between the respective cylinders will be maintainedthus avoiding the possibility of increased vibration. Further, thispulsed form of capacity modulation will result in alternating periodsduring which the driving motor is either operating at full load orsubstantially reduced loading. Thus it is possible to incorporateadditional apparatus to vary one or more of the operating parameters ofthe motor during the reduce load period of operation thereby furtherimproving system efficiency as discussed in greater detail below.

FIG. 4 graphically represents the benefits that the present inventionmay offer in maintaining tighter temperature control in a refrigeratedstorage case for example. Note how the temperature curve 55 of theinvention exhibits considerably less fluctuation than the correspondingtemperature curve 57 of a conventional controller.

It should be noted that valve assembly 48 will be activated between openand closed positions in a pulsed manner to provide the desired capacitymodulation. Preferably, the cycle time duration will be substantiallyless than the time constant of the system load which typically may be inthe range of about one to several minutes. In a preferred embodiment,the cycle time may be as much as 4 to 8 times less than the thermal timeconstant of the load or even greater. The thermal time constant ofsystem may be defined as the length of time the compressor is requiredto run in order to enable the system to cool the load from an upperlimit temperature at which the system is set to turn on, down to a pointat which the evaporator pressure reaches a lower limit at which thecompressor is shut down. More specifically, in a typical refrigerationsystem, flow of compressed fluid to the evaporator is controlled by atemperature responsive solenoid valve and operation of the compressor iscontrolled in response to evaporator pressure. Thus in a typical cycle,when the temperature in the cooled space reaches a predetermined upperlimit, the solenoid valve opens allowing compressed fluid to flow to theevaporator to begin cooling the space. As the compressed fluid continuesto flow to the evaporator and absorb heat, the pressure in theevaporator will increase to a point at which the compressor is actuated.When the temperature in the cooled spaces reaches a predetermined lowerlimit, the solenoid valve will be closed thereby stopping further flowof compressed fluid to the evaporator but the compressor will continueto run to pump down the evaporator. When the pressure in the evaporatorreaches a predetermined lower limit, the compressor will be shut down.Thus, the actual running time of the compressor is the thermal timeconstant of the load.

By use of this pulse width modulated blocked suction system, it ispossible to optimize compressor run times which minimizes the number ofon/off cycles and provides excellent load capacity matching and superiortemperature control for the area being cooled along with improvedoverall system efficiency as compared to conventional capacitymodulation systems. As is illustrated in FIG. 4, the pulse widthmodulated capacity compressor of the present invention enables extremelytight control of temperature as compared to conventional capacitymodulation systems. When applied to refrigeration systems, this tighttemperature control enables the average operating temperature to be setat a level more closely approaching the upper acceptable temperaturelimit whereas with conventional systems, the average operatingtemperature must be set well below the upper acceptable temperaturelimit so as to avoid the larger temperature swings encountered thereinfrom exceeding this upper acceptable limit. Not only does the use of ahigher average operating temperature result in substantial direct energycost savings but the higher average operating temperature maintains thedew point of the enclosed space at a higher level thus greatly reducingthe formation of frost. Similarly, when applied to air conditioningsystems, the pulse width modulated compressor of the present inventionenables the temperature of the conditional space to be controlled withina much smaller range than with conventional systems thus greatlyenhancing the comfort level of the occupants of such space. Evenfurther, this capacity modulation system may also be advantageouslyapplied to air compressor applications. Because of the ability of thecompressor to very closely track the load (which in air compressorapplications will be the volume of air being used at a desiredpressure), it is possible to greatly reduce the size of the pressurevessel if not completely eliminate same. Further, in airconditioningapplications additional energy savings may be realized because thecompressor is able to very closely match the load. This results in lowercondensing temperatures and hence pressures which means that thepressure against which the compressor is working is lower.

In most air conditioning and refrigeration compressors, the suction gasflow operates to cool the motor prior to compression. Because presentlyexisting blocked suction type capacity modulation systems operate toprevent flow of suction gas to the compression chamber the compressorcannot be operated in a reduced capacity mode for an extended periodwithout overheating of the compressor motor. The present invention,however, offers the additional advantage of greatly reducing thisoverheating possibility because the relatively cool suction gas issupplied to the cylinders on a rapidly cycling basis. This enables suchcompressors to operate at reduced capacity for substantially longer timeperiods thus also contributing to its ability to provide tightertemperature control of the spaces being cooled on a continuous basis aswell as reduced frost build-up in low temperature refrigerationapplications.

In determining the desired cycle frequency as well as the duration ofthe duty cycle or time period during which suction gas is to be suppliedto the compressor, it is generally desirable to first select a cycletime which is as long as possible but yet minimizes suction pressurefluctuations. Next the duty cycle will be determined which will besufficiently high so as to satisfy the load. Obviously, the duty cycleand cycle time are interrelated and other factors must also be takeninto account in selection thereof. For example, while it is desirable tomake the cycle time as long as possible, it can not be so long that thetime period during which suction gas flow is interrupted results inexcessive heating of the compressor motor.

While the capacity modulation system of the present invention has beendescribed above with reference to a multicylinder reciprocating pistontype compressor, it is also equally applicable to other types ofcompressors such as, for example, a rotary type compressor or a scrollcompressor. A rotary type compressor incorporating the capacitymodulation system of the present invention is illustrated in and will bedescribed with reference to FIGS. 5 and 6 and a scroll compressorincorporating same is illustrated and will be described with referenceto FIG. 7.

As shown in FIG. 5, a hermetic rotary type compressor 54 includes anouter shell 56 within which is disposed a compressor assembly and adriving motor 58 incorporating a stator 60 and rotor 62. Rotor 62 isrotatably supported by and fixed to crankshaft 66 which in turn isrotatably supported by upper and lower bearings 68 and 70. A compressionrotor 72 is eccentrically mounted on and adapted to be driven bycrankshaft 66. Compression rotor 72 is disposed within cylinder 74provided in housing 76 and cooperates with vane 78 (shown in FIG. 6) tocompress fluid drawn into cylinder 74 through inlet passage 80. Inletpassage 80 is connected to suction fitting 82 provided in shell 56 toprovide a supply of suction gas to compressor 54. As thus far described,rotary compressor 54 is typical of rotary type refrigeration and airconditioning compressors.

In order to incorporate the pulse width capacity modulation system ofthe present invention into rotary compressor 54, a valve assembly 84 isprovided being disposed within shell 56 and between suction fitting 82and suction gas flow path inlet passage 80. Operation of valve assembly84 is controlled by a control module 86 which receives signals from oneor more sensors 88 indicative of the system operating conditions.

Operation of valve assembly 84, control module 86 and sensors 88 will besubstantially identical to that described above with valve assembly 84operating under the control of control module 86 to cyclically open andclose to thereby modulate the flow of suction gas into cylinder 74. Aswith compressor 10, both the cycle frequency as well as the relativeduration of the open and closed portions of the cycle may be varied bycontrol module 86 in response to system operating conditions whereby thesystem efficiency may be maximized and the capacity varied to anydesired capacity between zero and full load.

FIG. 7 shows a scroll type compressor 144 which includes a compressorassembly 146 and a driving motor 148 both disposed within hermetic shell150.

Compressor assembly 146 includes a mean hearing housing 152 securedwithin and supported by outer shell 150, an orbiting scroll member 154movably supported on bearing housing 152 and a nonorbiting scroll member156 axially movably secured to bearing housing 152. Scroll members 154and 156 each include end plates 158 and 160 from which interleavedspiral wraps 162 and 164 extend outwardly. Spiral wraps 162 and 164together with end plates 158 and 160 cooperate to define moving fluidpockets 166, 168 which decrease in size as they move from a radiallyouter position to a radially inner position in response to relativeorbital movement between scroll members 154 and 156. Fluid compressedwithin the moving fluid pockets 166, 168 is discharged through acentrally located discharge passage 170 provided in nonorbiting scrollmember 156 into a discharge chamber 172 defined by the upper portion ofhermetic shell 150 and muffler plate 174 and thereafter is supplied tothe system via discharge fitting 176. An Oldham coupling is alsoprovided acting between scroll members 154 and 156 to prevent relativerotation therebetween.

A drive shaft 180 is also provided being rotatably supported in bearinghousing 152 and having one end thereof drivingly coupled to orbitingscroll member 154. A motor rotor 182 is secured to drive shaft 180 andcooperates with motor stator 184 to rotatably drive drive shaft 180. Asthus far described, scroll compressor 144 is typical of scroll typecompressors and will operate to draw fluid to be compressed flowing intohermetic shell 150 via inlet 186 into the moving fluid pockets viasuction inlet 188 provided in nonorbiting scroll member 156, compresssame and discharge the compressed fluid into discharge chamber 172.

In order to incorporate the pulse width capacity modulation system intoscroll compressor 144, a valve assembly 190 is provided being positionedin overlying relationship to suction inlet 188 so as to be able toselectively control flow of fluid to be compressed into respectivemoving fluid pockets 166 and 168. Operation of valve assembly 190 iscontrolled by control module 192 in response to signals received fromone or more sensors 194 in substantially the same manner as describedabove. It should be noted that while the present invention has beenshown and described with reference to a scroll compressor in which thehermetic shell is substantially at suction pressure, it may also beeasily incorporated in other types of scroll compressors such as thosein which the interior is at discharge pressure or in which both scrollsrotate about radially offset axes.

As may now be appreciated, the pulsed capacity modulation system of thepresent invention is extremely well suited for a wide variety ofcompressors and is extremely effective in providing a full range ofmodulation at relatively low costs. It should be noted that if desiredthe pulsed capacity modulation system of the present invention may alsobe combined with any of the other known types of capacity modulationsystems for a particular application.

In the above embodiments, it is intended that the compressor continue tobe driven while in an unloaded condition. Obviously, the power requiredto drive the compressor when unloaded (no compression taking place) isconsiderably less than that required when the compressor is fullyloaded. Accordingly, it may be desirable to provide additional controlmeans operative to improve motor efficiency during these periods ofreduced load operation.

Such an embodiment is shown schematically in FIG. 8 which comprises amotor compressor 90 which may be of the type described above withrespect to FIG. 1, FIGS. 5 and 6, or FIG. 7 and includes a solenoidvalve assembly connected to a suction line which is operative toselectively block the flow of suction gas to the compressing mechanism.The solenoid valve assembly is intended to be controlled by a controlmodule 92 in response to system conditions sensed by sensors 94. As thusfar described, the system represents a schematic illustration of any ofthe embodiments described above. In order to improve efficiency of thedriving motor during reduced load operation, a motor control module 96is also provided which is connected to the compressor motor circuit vialine 98 and to control module 92 via line 100. It is contemplated thatmotor control module 96 will operate in response to a signal fromcontrol module 92 indicating that the compressor is being placed inreduced load operating condition. In response to this signal, motorcontrol module 96 will operate to vary one or more of the compressormotor operating parameters to thereby improve its efficiency during theperiod of reduced load. Such operating parameters are intended toinclude any variably controllable factors which affect motor operatingefficiency including voltage reduction or varying the runningcapacitance used for the auxiliary winding of a single phase motor. Oncecontrol module 92 signals motor control module 96 that the compressor isbeing returned to fully loaded operation, motor control module 96 willthen operate to restore the affected operating parameters to maximizemotor efficiency under full load operation. There may be some time lagbetween the closing of the solenoid valve assembly and the reducedloading on the compressor which will be primarily dependent upon thevolume of suction gas in the area between the solenoid valve assemblyand the compression chamber. As a result, it may be desirable to providefor an appropriate time delay before the motor operating parameter isadjusted for the reduced loading. Of course, it is desirable that thesolenoid valve assembly be positioned as close as possible to thecompression chamber so as to minimize this delayed reaction time.

It should also be noted that while each of the embodiments has beendescribed as incorporating a solenoid valve which operates to controlthe flow of pressurized discharge gas to the suction gas flow controlvalve for controlling suction gas flow, it is also possible tosubstitute other types of valves therefor such as, for example, solenoidvalves by themselves or any other suitable valving arrangement. It is,however, believed that the use of a solenoid valve for controlling theflow of a pressurized fluid such as discharge gas to the suction controlvalve is preferred because it allows for application of greateractuating forces to the suction gas control valve and hence fasteroperation thereof. An exemplary embodiment of such a valve assembly isshown and will be described with reference to FIG. 9 it being noted thatthis valve assembly may be used in any of the embodiments describedabove.

As shown in FIG. 9, valve assembly 102 comprises a solenoid controlvalve 106 and a pressure actuated valve 104.

Solenoid valve assembly control valve 106 includes a housing 108 withinwhich is provided a valve chamber 110 having a valve member 112 movablydisposed therein. A pressurized fluid supply line 114 opens into chamber110 adjacent one end thereof and a vent passage 116 opens outwardly fromchamber 110 adjacent the opposite end thereof. An outlet passage 118 isalso provided opening into chamber 110 approximately midway between theopposite ends thereof. Valve member 112 is secured to one end of plunger120 the other end of which extends axially movably along hermeticallysealed bore 121 about which a solenoid coil 122 is positioned. As shown,plunger 120 will be biased into the position shown in which valve member112 overlies and closes off pressurized fluid supply line 114 and outletpassage 118 is in open communication with vent passage 116. Whensolenoid coil 122 is energized, shaft plunger 120 will operate to movevalve member 112 into a position in which it overlies and closes offvent passage 116 and allows open communication between pressurized fluidsupply line 114 and outlet 118. The opposite end of pressurized fluidsupply line 114 will be connected to a suitable source of pressurizedfluid such as for example discharge gas from the compressor.

Pressure actuated valve assembly 104 includes a housing 124 having acylinder 126 provided therein within which piston 128 is movablydisposed. A shaft 130 has one end connected to piston 128 and extendsfrom cylinder 126 through bore 132 into a chamber 134 provided inhousing 124. A valve member 136 is secured to the end of shaft 130, ispositioned within chamber 134 and is movable by shaft 130 into and outof sealing engagement with valve seat 138 provided on partition 140 soas to selectively control flow of suction gas from chamber 134 intochamber 142 and then through outlet 144 outlet 145. An inlet 146 inlet147 is provided for supplying suction gas to chamber 134.

Fluid outlet line 118 opens into one end of cylinder 126 and serves toprovide pressurized fluid thereto to bias piston 128 in a direction suchthat valve 136 moves into sealing engagement with valve seat 138 tothereby interrupt the flow of suction gas from inlet 146 to outlet 144inlet 147 to outlet 145. A return spring 148 return spring 149 is alsoprovided within cylinder 126 which serves to bias piston 128 in adirection so as to move valve member 136 out of sealing engagement withvalve seat 138 in response to venting of the pressurized fluid fromcylinder 126.

In operation, when control module 50 determines that capacity modulationis in order, it will operate to energize solenoid control valve 106thereby moving valve 112 to the right as shown and allowing pressurizedfluid to flow through chamber 110 to cylinder 126. This pressurizedfluid then operates to move piston 128 in a direction to close valve 136thereby preventing further flow of suction gas to the compressionmechanism. When solenoid control valve 106 is deenergized by controlmodule 50, valve 112 will move into a position to interrupt the supplyof pressurized fluid to cylinder 126 and to vent same via passage 116thereby enabling return spring 148 return spring 149 to move piston 128in a direction to open valve member 136 such that the flow of suctiongas to the compressor is resumed.

It should be noted that valve assembly 102 is exemplary only and anyother suitable arrangement may be easily substituted therefor. As notedbefore, in order to facilitate rapid response to capacity modulationsignals, it is desirable that the suction flow shut off valve be locatedas close to the compression chamber as possible. Similarly, thepressurized fluid supply line and vent passages should be sized relativeto the volume of the actuating cylinder being supplied thereby to ensurerapid pressurization and venting of same.

It will be appreciated by those skilled in the art that various changesand modifications may be made to the embodiments discussed in thisspecification without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A capacity modulated compressor comprising: acompression mechanism having a compression chamber therein, a suctioninlet for supplying suction gas to the compression chamber and a movablemember operative to vary the volume of said compression chamber; a powersource operatively connected to effect movement of said movable memberto thereby compress gas drawn into said compression chamber through saidsuction inlet; a valve provided in the suction gas flow path to saidcompression mechanism, said valve being operable between open and closedpositions to cyclically allow and prevent flow of suction gas into saidcompression chamber; and control apparatus for actuating said valvebetween said open and closed positions, said control apparatus beingoperative to cycle said valve such that its cycle time is substantiallysmaller than the time constant of the load on said compressor.
 2. Acapacity modulated compressor as set forth in claim 1 wherein said valveis positioned in close proximity to said compression chamber.
 3. Acapacity modulated compressor as set forth in claim 1 wherein said valveis a bidirectional valve.
 4. A capacity modulated compressor as setforth in claim 1 wherein at least one of said cycle time and the timeduration said valve is in said closed position is varied in response tosensed operating conditions.
 5. A capacity modulated compressor as setforth in claim 4 wherein said power source continues to effect movementof said movable member as said valve is cycled between said open andclosed positions.
 6. A capacity modulated compressor as set forth inclaim 4 wherein said cycle time and said time duration are varied inresponse to said sensed operating condition.
 7. A capacity modulatedcompressor as set forth in claim 1 wherein said valve is actuated bypressurized fluid.
 8. A capacity modulated compressor as set forth inclaim 7 further comprising a control valve operative to control the flowof pressurized fluid to said valve.
 9. A capacity modulated compressoras set forth in claim 8 wherein said control valve is a solenoidactuated valve.
 10. A capacity modulated compressor as set forth inclaim 7 wherein said pressurized fluid is supplied from said compressionmechanism.
 11. A capacity modulated compressor as set forth in claim 1wherein said power source comprises an electric motor.
 12. A capacitymodulated compressor as set forth in claim 11 wherein said controlmodule operates to vary an operating parameter of said electric motorwhen said valve is in said closed position so as to thereby improve theoperating efficiency of said motor.
 13. A capacity modulated compressoras set forth in claim 12 wherein said operating parameter of said motoris varied a predetermined time period after said valve is moved to saidclosed position.
 14. A capacity modulated compressor as set forth inclaim 1 wherein said compression mechanism is a reciprocating pistoncompressor.
 15. A capacity modulated compressor as set forth in claim 14wherein said reciprocating piston compressor includes a plurality ofpistons and cylinders, said valve being operative to prevent flow ofsuction gas to all of said cylinders.
 16. A capacity modulatedcompressor as set forth in claim 15 wherein said valve operates toprevent flow of suction gas to all of said cylinders simultaneously. 17.A capacity modulated compressor comprising: a hermetic shell; acompression mechanism disposed within said shell, said compressionmechanism including a compression chamber defined in part by a moveablemember, said moveable member operating to vary the volume thereof; adrive shaft rotatably supported within said shell and drivingly coupledto said movable member; a suction inlet passage for supplying suctiongas to said compression chamber from a source remote from said shell; avalve within said suction inlet passage, said valve being actuablebetween an open position to allow flow of suction gas through said inletpassage and a closed position to substantially prevent flow of suctiongas through said inlet passage; a controller for cyclically actuatingsaid valve to an open position for first predetermined time periods andto a closed position for second predetermined time periods, the ratio ofsaid first predetermined time period to the sum of said first and secondpredetermined time periods being less than a given load time constantand determining the percentage modulation of the capacity of saidcompressor.
 18. A capacity modulated compressor as set forth in claim 17wherein said valve is a bidirectional valve and is actuable to saidclosed position by pressurized fluid.
 19. A capacity modulatedcompressor as set forth in claim 18 further comprising a solenoid valveactuable by said controller to control flow of said pressurized fluid tosaid valve.
 20. A capacity modulated compressor as set forth in claim 19wherein said pressurized fluid is discharge gas from said compressor.21. A capacity modulated compressor as set forth in claim 17 whereinsaid valve is positioned in close proximity to said compression chamber.22. A capacity modulated compressor as set forth in claim 17 whereinsaid compressor is a refrigeration compressor.
 23. A capacity modulatedcompressor as set forth in claim 17 wherein said compressor is an aircompressor.
 24. A capacity modulated compressor as set forth in claim 17wherein said compressor is a rotary compressor.
 25. A capacity modulatedcompressor as set forth in claim 17 wherein said compressor is a scrollcompressor.
 26. A capacity modulated compressor as set forth in claim 17wherein said sum of said first and second time periods is less than onehalf of said load time constant.
 27. A capacity modulated compressor asset forth in claim 17 further comprising a motor for rotatably drivingsaid drive shaft, said valve being actuable between said open and closedpositions while said motor continues to rotatably drive said driveshaft.
 28. A capacity modulated compressor as set forth in claim 27wherein said controller operates to vary an operating parameter of saidmotor between periods in which said valve is in said closed position andin said open position to thereby improve the operating efficiency ofsaid motor.
 29. A method of modulating the capacity of a compressorforming a part of a cooling system to accommodate varying cooling loadconditions comprising: sensing an operating parameter of said coolingsystem, said parameter being indicative of the system load; determininga cycle frequency of a maximum duration which will minimize variation inthe suction pressure of refrigerant being supplied to said compressor;determining a first time period during which suction gas will besupplied to said compressor and determining a second time period duringwhich suction gas will be prevented from flowing to said compressor,said first and second time periods being equal to said cycle frequency;and pulsing a valve between open and closed positions for said first andsecond time periods respectively to thereby modulate the capacity ofsaid compressor in response to said system operating parameter.
 30. Acapacity modulated compressor comprising: a compression mechanism havinga compression chamber therein, a suction inlet for supplying suction gasto the compression chamber and a movable member operative to vary thevolume of said compression chamber; a power source operatively connectedto effect movement of said movable member to thereby compress gas drawninto said compression chamber through said suction inlet; a valveprovided in the suction gas flow path to said compression mechanism andactuated by pressurized fluid, said valve being operable between openand closed positions to cyclically allow and prevent flow of suction gasinto said compression chamber; and control apparatus for actuating saidvalve between said open and closed positions, said control apparatusbeing operative to cycle said valve such that its cycle time issubstantially smaller than the time constant of the load on saidcompressor.
 31. A capacity modulated compressor as set forth in claim 30further comprising a control valve operative to control the flow ofpressurized fluid to said valve.
 32. A capacity modulated compressor asset forth in claim 31 wherein said control valve is a solenoid actuatedvalve.
 33. A capacity modulated compressor as set forth in claim 30wherein said pressurized fluid is supplied from said compressionmechanism.
 34. A capacity modulated compressor comprising: a compressionmechanism having a compression chamber therein, a suction inlet forsupplying suction gas to the compression chamber and a movable memberoperative to vary the volume of said compression chamber; an electricmotor operatively connected to effect movement of said movable member tothereby compress gas drawn into said compression chamber through saidsuction inlet; a valve provided in the suction gas flow path to saidcompression mechanism, said valve being operable between open and closedpositions to cyclically allow and prevent flow of suction gas into saidcompression chamber; and a control apparatus for actuating said valvebetween said open and closed positions, said control apparatus beingoperative to cycle said valve such that its cycle time is substantiallysmaller than the time constant of the load on said compressor andoperable to vary an operating parameter of said electric motor when saidvalve is in said closed position so as to thereby improve the operatingefficiency of said motor.
 35. A capacity modulated compressor as setforth in claim 34 wherein said operating parameter of said motor isvaried a predetermined time period after said valve is moved to saidclosed position.
 36. A capacity modulated compressor comprising: ahermetic shell; a compression mechanism disposed within said shell, saidcompression mechanism including a compression chamber defined in part bya movable member, said movable member operating to vary the volumethereof; a drive shaft rotatably supported within said shell anddrivingly coupled to said movable member; a suction inlet passage forsupplying suction gas to said compression chamber from a source remotefrom said shell; a valve within said suction inlet passage, said valvebeing actuable between an open position to allow flow of suction gasthrough said inlet passage and a closed position to substantiallyprevent flow of suction gas through said inlet passage, said valve beinga bidirectional valve actuable to said closed position by pressurizedfluid; and a controller for cyclically actuating said valve to an openposition for first predetermined time periods and to a closed positionfor second predetermined time periods, the ratio of said firstpredetermined time period to the sum of said first and secondpredetermined time periods being less than a given load time constant,determining the percentage modulation of the capacity of saidcompressor.
 37. A capacity modulated compressor as set forth in claim 36further comprising a solenoid valve actuable by said controller tocontrol flow of said pressurized fluid to said valve.
 38. A capacitymodulated compressor as set forth in claim 37 wherein said pressurizedfluid is discharge gas from said compressor.
 39. A capacity modulatedcompressor comprising: a hermetic shell; a compression mechanismdisposed within said shell, said compression mechanism including acompression chamber defined in part by a movable member, said movablemember operating to vary the volume thereof; a drive shaft rotatablysupported within said shell and drivingly coupled to said movablemember; a suction inlet passage for supplying suction gas to saidcompression chamber from a source remote from said shell; a valve withinsaid suction inlet passage, said valve being actuable between an openposition to allow flow of suction gas through said inlet passage and aclosed position to substantially prevent flow of suction gas throughsaid inlet passage; a controller for cyclically actuating said valve toan open position for first predetermined time periods and to a closedposition for second predetermined time periods, the ratio of said firstpredetermined time period to the sum of said first and secondpredetermined time periods being less than a given load time constant,determining the percentage modulation of the capacity of saidcompressor; and a motor for rotatably driving said drive shaft, saidvalve being actuable between said open and closed positions while saidmotor continues to rotatably drive said drive shaft; wherein saidcontroller operates to vary an operating parameter of said motor betweenperiods in which said valve is in said closed position and in said openposition to thereby improve the operating efficiency of said motor. 40.A method of modulating the capacity of a compressor forming a part of acooling system to accommodate varying cooling load conditionscomprising: sensing an operating parameter of said cooling system, saidparameter being indicative of the system load; determining a cyclefrequency of a maximum duration which will minimize variation in thesuction pressure of refrigerant being supplied to said compressor;determining a first time period during which suction gas will besupplied to said compressor and determining a second time period duringwhich suction gas will be prevented from flowing to said compressor,said first and second time periods being equal to said cycle frequency;and pulsing a valve between open and closed positions for said first andsecond time periods respectively to thereby modulate the capacity ofsaid compressor in response to said system operating parameter.